In the method of producing an extract and/or a squeezed liquid from a food to be extracted and/or squeezed, as a representative example for industrial production of a regular coffee extract, a method of extracting a prescribed amount of a crushed material of roasted coffee beans with hot water using a closed extract column, a kneader, or the like is commonly employed. After roasting, coffee beans are crushed by a grinder or the like. In the paper filter drip method for household use, the coffee beans are milled into an extent of approximately 400 μm. Whereas, in the case of dripping industrially using a kneader and an extract column, since a fine powder causes clogging, in many cases, removal of the fine powder is carried out in advance using a sifter or the like to unify the particle size at the time of crushing to approximately 3 to 5 mm. Thereafter, the crushed beans are held in hot water at about 90° C. for several minutes and then subjected to solid-liquid separation by means of spontaneous drop using a flannel, a mesh filter, or the like.
However, according to the above-mentioned method, oxidation quickly occurs since the extract operation must be repeated for every batch and due to high temperatures, which results in deterioration in flavor and loss of aroma fragrant components. Furthermore, when the scale becomes large, it takes a long time to completely drain the liquid. In general, the residue is transferred in a disposal step after several minutes. However, the residue does not reach the state where the liquid is sufficiently drained but contains water of five times or more that of the time of drying. Thus, in order to sufficiently recover the coffee extract, warm water or the like is sprinkled in some cases. For achieving this operation, it takes several tens of minutes, and liquid draining of the ultimate residue after solid-liquid separation is still insufficient. Accordingly, in all cases, problems such as putrefaction in the disposal works and a burden in transport costs remain.
In the light of the above, according to this method, it is impossible to continuously obtain useful components with good flavor within a short period of time by keeping high extraction efficiency and squeezing efficiency at low temperatures in the treatment technologies of extraction and/or squeezing and solid-liquid separation. Also, the residue following the solid-liquid separation is not sufficiently dehydrated. Accordingly, this method is far from a method which reduce the labor and costs of disposal, and it cannot be said that this method is desirable for the production process from the viewpoints of product quality, improvement in works, and preservation of the environment.
The present applicant already reported a method for producing an extract and/or a squeezed liquid, which comprises feeding a food to be extracted and/or squeezed into a crushing apparatus having a narrow gap, adding a low-temperature solvent of lower than 60° C. thereto immediately after crushing and/or simultaneously with crushing and treating the food within the apparatus to extract and/or squeeze a useful food component into the solvent, followed by removing the resulting extracted residue and/or squeezed residue, if necessary (see JP-A-2003-225054).
According to the publication, it is possible to continuously obtain a solid-liquid suspension comprising a useful component with good flavor in a short time by keeping high extraction efficiency and squeezing efficiency at low temperatures in the processing technologies of extraction and/or squeezing. However, with respect to the solid-liquid separation method of a solid-liquid suspension, specifically, it is merely described in the working examples that centrifugation is carried out at 750 G for 10 minutes, but the degree of dehydration of the residue after solid-liquid separation is unclear. The publication does not mention at all whether the production method is desirable from the viewpoint of preservation by which the labor and costs of disposal of the residue can be reduced.
Also, there is reported a method for extracting an effective component of coffee by feeding roasted coffee beans into a twin-screw extruder and pressing the coffee beans with added hot water to separate the extracted liquid containing water-soluble components in the coffee beans from a residue (see JP-A-62-126935).
The invention of this publication relates to a method for extracting coffee in which a concentrated liquid which is little dissipation of flavor components is rationally obtained. Since the amount of hot water to be added is kept to a minimum necessary for the extraction, the recovered concentrated liquid is strong so that it can be directly used as the raw material for instant coffee. The concentrated liquid is obtained by extracting the water-soluble components in the coffee beans into the hot water by the heat and pressure of the extruder and squeezing out of the extruder through a gap in a slit barrel, provided at a proper position, by forward compression force. The residue of coffee beans from which the water-soluble components have been extracted is directly pushed out from a discharge port in the forward end of the extruder.
Accordingly, since this method is concerned with the extraction using a minimum amount of high-temperature hot water under high pressure in an extruder, it has an advantage that the extracted residue is dehydrated to some extent. However, this method does not avoid deterioration in flavor by rapid oxidation of the coffee beans caused by high temperature.
According to the above-mentioned conventional methods, it is extremely difficult to efficiently and continuously extract and/or squeeze soluble solid components from a food to be extracted and/or squeezed particularly with a solvent in a low temperature region quickly after crushing. Accordingly, milling is needed, and the subsequent work such as solid-liquid separation cannot be carried out quickly and continuously by the conventional methods on an industrial scale.
Furthermore, the method for producing a coffee extract which contains high fat was reported (see JP-A-11-075694). The publication discloses a method for the production of a coffee extract which contains high fat by simultaneous crushing and extraction of coffee beans, which comprises mixing roasted and crudely crushed coffee beans with water and passing the mixed water through a wet medium grinder to further mill the coffee beans.
A coffee extract which contains high fat and is rich in flavor can be obtained by using a wet medium grinder comprising a specific constitution. However, since coffee beans are crudely crushed before milling, coffee flavor dissipates and the resulting coffee extract liquid contains less flavor.